This study aimed at assessing the characteristics of water hyacinth biomass in Lake Tana. Explanatory research design was used based on biomass samples and satellite images acquired along with field observation and literature reviews. The results showed that high amount of N and P nutrients, shallow nature of the Lake and suitable climatic conditions of the area are the causes for the weeds’ proliferation. The mean NDVI values were −0.542 to 0.828 and −0.628 to 0.877 in the dry and wet seasons, respectively. The spatial distribution of the weed was 2126.9 ha and 592.4 ha during the wet and dry seasons. The weed has recorded a mean leaf length of 9.3 cm, petiole length of 28.1 cm, root shoot ratio of 3.3, leaf blade area of 55.6 cm2and leaf area index of 11343.9 cm2. In addition, a mean of 10.9 leaves per plant and 18.6 plants per 0.25m2was found. Furthermore, the biomass analysis revealed 1,990,787.8 tons of wet and 554,523.8 tons of dry water hyacinth biomass can be harvested from the Lake per year. Stakeholders shall work on control of water hyacinth biomass as a short-term measure and reduction of nutrient inflow into the Lake as a long-term measure.